Effect of valspodar coadministration on the paclitaxel brain levels in nude mice after intravenous injection of 8 mg/kg paclitaxel. Four hours before intravenous application the animals were treated with the vehicle of valspodar by mouth (control, open squares) or 50 mg/kg valspodar by mouth (valspodar group, filled squares). Brain levels for a valspodar group with reduced paclitaxel dose (4 mg/kg, open circles) were investigated 24 hours after intravenous injection. Means ± SEM, n = 3–4. Compared with the respective controls, all values in the valspodar groups were significantly (P ≤ 0.05) higher.